1. Field of the Invention
The present invention relates to a display device and a method for driving a display device, and more particularly to a display device displaying an image with applying a voltage to a plurality of wiring structures for driving and a method for driving a display, said method being intended for driving the display device.
2. Related Art
Conventionally liquid crystal display (LCD) devices are known as display devices for displaying such images as characters and figures in data processing devices such as personal computers. Liquid crystal displays are available in various types of different constructions. In recent years, active matrix driving liquid crystals are widely used. These employ thin film transistors (TFT) and the like, can accurately control the tone of images, and are suitable for the display of fast moving animated images.
For example, in TFT liquid crystal displays, a plurality of data lines and a plurality of gate lines are arranged so as to intersect each other on one of two opposing surfaces of a pair of transparent substrates made of a material such as glass and arranged opposite each other. A TFT is arranged at each position at which data lines and gate lines intersect. An electrode is formed on the other opposing surface of the transparent substrates. A liquid crystal is disposed between the pair of transparent substrates. Images are displayed on TFT liquid crystal displays with the application of voltage to gate lines to turn on a plurality of transistors one after another as well as with application of voltage corresponding to display images to data lines.
Since data lines, gate lines and electrodes are insulated from each other in liquid crystal displays, static electricity is liable to be generated. For example, friction from the wind in clean rooms in the manufacturing process of liquid crystal displays generates electricity. This static electricity is applied to a switching element such as a TFT as high voltage. A large current instantly flows due to discharge of electricity to the outside when probes are contacted in the inspection process, and the liquid crystal display is electrified overall, deteriorating and damaging the switching element. This has become a factor decreasing the manufacturing yield of liquid crystal displays.
To solve this problem, a proposal was made to cut off a portion where a short circuit line (below referred to as an external short circuit line) is provided on the external periphery of an area on a transparent substrate where a switching element is provided with data lines and gate lines connected to the external short circuit line. In the above example, in the stage before the external short circuit wire is cut off, it is possible to prevent high voltage from being applied to the switching element, but between the time that the portion where the external short circuit line is formed is cut off and the time that the LCD is installed in the device and made to contact the LCD driver and the like, the switching element can be deteriorated and damaged by static electricity. Thus it is not sufficient as a countermeasure against static electricity.
In addition, PUPA 63-85586 and PUPA 3-134628 propose that a short circuit line (herein referred to as internal short circuit line) is formed which is not on the above cut off portion in an external periphery area of the transparent substrate where the switching element is provided. In order to avoid an unfavorable effect of the internal short circuit line when the internal short circuit line is driven, a proposal is made to connect the above internal short circuit line, data lines and gate lines via a connecting element.
However, the above design has the drawback of increasing the overall power consumption of the liquid crystal display because the resistance of the connecting element consumes power when voltage is applied to data lines and gate lines for displaying images on the liquid crystal display.
As an example, a liquid crystal display with 640.times.480 pixels which can display color images includes 1920 data lines and 480 gate lines. As shown in FIG. 7, data lines, gate lines and the internal short circuit wire are respectively connected to this liquid crystal display via a connecting element with a resistance of 200 k.OMEGA.. A voltage of 5 to 15 V is applied to data lines in accordance with the display image. To gate lines that are turned on a voltage of +30 V is applied and to other gate lines a voltage of 0 V is applied to display images. The average value of voltage applied to data lines and gate lines becomes about +10 V and about 0 V respectively. The synthesized resistance connected to data lines is about 200 k.OMEGA., but the total effective resistance is only about 100.OMEGA. because 1920 resistances of 200 k.OMEGA. are connected in parallel. The synthesized resistance connected to gate lines is 300 k.OMEGA. but the total effective resistance becomes about 400.OMEGA. because 280 resistances of 300 k.OMEGA. are connected in parallel. Thus an equivalent circuit like that shown in FIG. 7 is provided. The power consumption P by all the resistances is: EQU power of consumption P=V.sup.2 .div.R=(10V).sup.2 .div.500.OMEGA.=0.2W
Consequently, in the above equation, power consumption of P (=0.2 W) is added to the power consumption of the main body of the liquid crystal display.
In particular, reduction in power consumption is an important issue in electronic devices like portable computers that allow operation by batteries, in consideration of portability. Liquid crystal displays to be mounted on such electronic devices must be low in power consumption. The power consumption of the main body of liquid crystal displays mounted on electronic devices like portable computers is about 0.6 W. The power consumption P caused by the resistance described above is very large with respect to the power consumption of the liquid crystal display. In addition, when the electric resistance value is heightened to reduce the power consumption P, the effectiveness against static electricity is lowered.
Furthermore, PUPA 3-134628 describes that non-linear elements like diodes that provide low resistance on the order of several k.OMEGA. are used with respect to high voltages of 70 through 80 V in the connecting element described above. In any case electric power is consumed at the connecting element, and power consumption cannot be sufficiently reduced.